1. Field of the Invention
The present invention relates to a reflection plate achieving a high contrast, a manufacturing method thereof, a liquid crystal display device, and a manufacturing method thereof.
2. Description of the Related Art
There has been known a reflection type liquid crystal display device, which reflects incident light coming from outside with a reflection plate included therein, to use the light as the light source for display. The reflection type liquid crystal display device does not require backlight as a light source. Therefore, the reflection type liquid crystal display device can be more decreased in power consumption and more thinned than a transmission type liquid crystal display device, and thus is used in portable phones, etc.
The reflection type liquid crystal display device comprises liquid crystal sealed in a liquid crystal cell, switching elements for driving the liquid crystal, and a reflection plate which is provided inside or outside the liquid crystal cell. The reflection type liquid crystal display device is an active matrix type liquid crystal display device employing thin film transistors as switching elements, for example.
A liquid crystal display device, which comprises a reflection plate on whose surface a reflection electrode having uneven patterns is formed in order to increase light to be scattered toward the normal line direction of the reflection plate (toward the viewer) and thereby to improve the contrast, is developed as a reflection type liquid crystal display device. Such a liquid crystal display device is disclosed in Japanese Patent No. 2825713, and other publications.
In this liquid crystal display device, the wavy patterns are formed by arranging a plurality of cylindrical protruding portions made of resin, under a light reflection layer. This light reflection layer is formed on the reflection plate on which the protruding patterns arc formed, via an organic insulation film. As illustrated in a plan view shown in FIG. 21, the plurality of protruding patterns each having a circular-shaped cross section, are arranged on the surface of the reflection plate independently from one another. The protruding patterns having a circular-shaped cross section have a high light scattering characteristic, and reflect incident light almost uniformly toward the entire azimuth angle.
The polar angle is an angle φ1 shown in FIG. 22 measured from the normal line direction of the reflection plate, while the azimuth angle is an angle φ2 measured in the plane parallel to the reflection layer. Generally, reflection characteristics (azimuth angle, polar angle, intensity) of a reflection plate are observed by examining reflection light of incident light coming from a direction of a −30-degree polar angle.
A reflection plate acquiring a high reflection light intensity toward the direction of a 0-degree polar angle (toward the normal line direction) is demanded from a viewpoint of improving the contrast of a liquid crystal display device when it is used. However, a reflection plate having protruding patterns like the one shown in FIG. 21 reflects light almost uniformly toward the entire azimuth angle. Accordingly, the relationship between the polar angle and the reflection light intensity shows a state similar to normal distribution, as shown by a graph of FIG. 23. Therefore, there has existed a limit on how much the reflection light intensity can be improved toward the direction of the 0-degree polar angle, with the use of such protruding patterns having a circular-shaped cross section.
Not only the reflection type liquid crystal display device, but a so-called semi-transparent liquid crystal display device, such as disclosed in Japanese Patent No. 2955277, has the same problem. This liquid crystal display device comprises pixel electrodes having a transparent region and a reflection region, and a reflection plate, and thus has both of the transmission function and the reflection function. As having the reflection plate, this type of liquid crystal display device cannot avoid the same problem.